This invention relates to a system for evenly spreading within a semicondcutor processing chamber gas, particularly such gases as used in chemical vapor deposition (CVD) of very thin layers of material uniformly over and across the surfaces of large diameter wafers.
This invention relates to a system for evenly spreading within a semicondcutor processing chamber gas, particularly such gases as used in chemical vapor deposition (CVD) of very thin layers of material uniformly over and across the surfaces of large diameter wafers.
In chemical vapor deposition (CVD) of material onto semiconductor wafers, a processing gas or gases are admitted into a sealed chamber (a process well known in the art)
to insure even deposition of material onto a wafer, which is held in position on a platform within the chamber, the processing gas should be distributed as it flows into the chamber so that the gas flows uniformly onto and over the wafer. Thus a layer of solid material being deposited on the wafer is even and uniform across the wafer. As wafers of larger and larger diameter (e.g., 300 mm), and much greater device density (e.g., line widths of 170 nanometers or finer) become standard, it is more important than ever that processing gas flow onto and over the wafers be as nearly perfect in uniformity as possible.
Various ways of evenly distributing processing gas have been used in the past. One commonly used way is to flow the gas through xe2x80x9ca shower headxe2x80x9d located at the gas inlet to the chamber. A disadvantage of such an arrangement is that it tends to be bulky and costly. Moreover, fine holes through the shower head tend to clog and must be cleaned frequently. The present invention provides a simple and efficient way of obtaining uniformity of gas flow.
The present invention, in one aspect, provides a mechanical device, termed herein an impeller, in an inlet gas passageway leading into a wafer processing chamber. The impeller, which is stationary, imparts a spinning or whirlpool-like flow to the processing gas within a lower portion of the passageway so that as the spinning gas flows out of the passageway and enters the chamber, centrifugal forces impart radial movement to the gas flow along with downward movement into the chamber. This combined radial and downward movement helps facilitate relatively uniform distribution of gas onto and over a wafer being processed. The impeller has fixed, fan-like blades which overlap. A slight tilt of the blades provides a slot between a front edge of one blade and a back edge of the next one, and so on. Thus gas flowing down and through the slots between the blades into the lower portion of the passageway has a spinning, or whirlpool-like motion imparted to it.
(Claim 1) Viewed from a first apparatus aspect, the present invention is a semiconductor processing apparatus comprising a chamber, a wafer support member within the chamber, a gas inlet pipe for flowing processing gas down into a top part of the chamber at an exit-end of the pipe; and an impeller mounted within the pipe above the exit-end thereof, the impeller directing the gas flowing down within the pipe into a plurality of lateral secondary gas streams rotating beneath the impeller to cause a swirling whirlpool-like motion of the gas.
Viewed from a second apparatus aspect, the present invention is semiconductor apparatus useful to control processing gas flowing onto a wafer held within the chamber. The apparatus comprises. The apparatus comprises a chamber having an upper portion and a lower portion, a platform for holding a wafer for the processing thereof within the chamber, a gas pipe for flowing processing gas down through an exit-end thereof into the upper portion of the chamber, and an impeller. The comprises a plurality of fan-like blades radiating from a center to an outer rim. Thee blades are circumferentially spaced and overlap each other with a front edge of one blade being beneath and ahead of a rear edge of the next blade and so on. There are respective spaces between the blades where they overlap. The spaces between the blades forming secondary gas passageways for directing respective streams of gas laterally beneath the impeller into a rotational swirling motion. The impeller is fixed within the gas pipe above its exit-end such that when the swirling gas beneath the impeller flows into the upper portion of the chamber internal forces cause the gas to flow outward across the chamber and then down evenly onto and over a wafer on the platform.
Viewed from a method aspect, the invention is a method of evenly spreading processing gas onto and over the surface of a semiconductor wafer. The method comprising the steps of: flowing a stream of processing gas in a pipe downward toward a wafer being held in a chamber; generating a whirlpool-like laterally swirling motion in the gas stream; and using internal forces within the swirling gas to cause it on entering the chamber to flow immediately outward within the chamber and then down evenly onto and over a wafer within the chamber.
A better understanding of the invention together with a fuller appreciation of its many advantages will best be gained from a study of the following description given in conjunction with the accompanying drawings and claims.